the dark, cooler shape thrown when something blocks the light: a shadow or patch of shade, and by extension the protection or the fleeting quality that a shadow stands for
In a land baked by the sun, shade was first of all a physical relief: the cool dark under a tree, a rock, a roof, or a booth where a person could survive the heat of the day. That single concrete picture is the seed of everything else this word does. Because a shadow is cast by something larger that stands between you and the burning sun, to be in someone's shadow came to mean being under their protection. And because a shadow shifts, stretches, and finally disappears as the day ends, the same word became one of the Bible's favorite images for how short and how fragile a human life is.
These are not separate, unrelated words that happen to be spelled alike. They are one image seen from different angles. The shade of a tree, the shelter of a king's or God's outstretched wing, and the shadow that lengthens toward nightfall all draw on the same everyday experience of standing in the dark patch that a tall thing throws. A reader can move from one to the next without changing the underlying picture, which is why the standard lexicons keep them under one entry rather than splitting them into homonyms.
The word also names one very specific thing: the shadow on a stairway used to mark the passing hours, in the sign given to King Hezekiah. That use sits a little apart from the rest, since here the shadow is simply a moving marker of time rather than relief, refuge, or a figure of mortality.
Writers could even fold two of these senses together on purpose. When the Bible says wisdom and money each give a shadow, it is playing on both the protective sense (a shadow shelters you) and the fleeting sense (a shadow does not last), letting one short line carry both at once.